"When I approached her for it, she said, ‘Well, we’re going to sing live.’ I said, ‘You’ll sing live because I don’t sing.’ And she said, ‘No, no, what I can’t stand in movies is when you see playback and that they’re lip-syncing. We’re going to sing live.’ I knew we were going to have to do that, and luckily I had time and I had wonderful support," the actor and director shared, adding that the Joanne performer only agreed to sign on to the movie if Cooper fully committed to the music.

"She said, 'You’re going to become a musician and you’re going to make me as comfortable as you can onscreen,'" he explained, sharing that the pop star, who he called "kind of a revelation," helped ease him into the role of a musician.

Singing solo on stage "was the scariest thing," Cooper said. "Either you feel comfortable on a stage or you don’t. And it really paid off."

While filming the movie, which is a remake of the 1976 classic starring Barbra Streisand (itself a remake of the 1937 film), the two performed at real-life festivals in 2017, including Stagecoach, Coachella and Glastonbury.